1. Field of the Invention
The present invention relates to a data processor, and more specifically to improvement of a single chip microcomputer capable of treating a processing request (namely, interrupt request) sent in an asynchronous manner from a device external to a central processing unit (called "CPU" in the specification)
2. Description of Related Art
Data processors including microcomputers are adapted to process a series of data by sequentially reading and executing a program stored in a memory. In response to a processing request other than an ordinary programed processing, the data processors generally operate to acknowledge an interrupt request, and to interrupt execution of a program which is been executed when the interrupt request is received, and further to read and execute a program corresponding to the acknowledged interrupt request.
In conventional data processors, actually, after the interrupt request is sent to the CPU from an external device (namely, an interrupt source), the data processor operates to save contents of a program counter and a program status word, and also to save contents of general purpose registers and initialize the general purpose registers. Thereafter, the data processor starts an interrupt subroutine corresponding to the interrupt request. Accordingly, a long time is consumed after the interrupt request is sent to the CPU until the interrupt program is actually executed. Particularly, the saving of the program counter and the program status word, and the saving and initialization of the general purpose registers are a matter foreign to the data processing required for the interrupt processing. As a result, the interrupt will greatly decrease the data processing capacity of the CPU in the conventional data processor.